I mostly use OPUS nowadays. Just download a podcast/audiobook/whatever, convert it to 32 kbps (which even is redundant! even lower is totally Okay, 24 kbps still can sound subjectively lossless for human speech, 16 kbps will probably be still good yet audibly different) OPUS with the voip profile and fit tons of content to listen to offline on whatever a humble storage your portable device has left.
OPUS really saves the day as today smartphones storage usually is filled with high-quality pictures and videos you have taken and apps getting gigger and bigger every year.
I wish Apple would introduce first-class OPUS support in the M4B container in iTunes but as long as it doesn't (and I doubt it ever will) 3-rd party audiobook players do a great job.
On iPhone we use "MP3 Audiobook Player Pro"[1]. Despite saying "MP3" in its title it supports many formats including OPUS. They broke OPUS speed-up and hadn't fixed it for some time but have fixed it recently so it's great again.
On Android "Smart AudioBook Player"[2] does a perfect job.
Not OP, but I have all mine stored on my plex server, and use Prologue to access them on iOS devices and like it a lot. https://apps.apple.com/app/id1459223267
Sadly my old "64 MB" (not really, it's 128 MB IIRC) player doesn't support OPUS. It's there where I have to fallback to AAC or MP3. But it luckily supports FLAC and Vorbis (which weren't listed in the specs) so I have some FLACs and OGGs on it as well. It also lacks speed adjustment so I had to pree-upspeed books with Audacity during the days when first Android devices were a luxury thing. If only it had support for OPUS, pitch-preserving speed adjustment and position persistance it could indeed make a great audiobook/podcast listening device.
Ogg and Opus will never have much adoption on the web as long as Apple devices exist. I don't think any single tech company has managed to be as destructive to the proliferation of patent-unencumbered formats in the short history of computing.
Opus hasn't caught on for music and podcasts, but is very popular in some other areas. YouTube uses Opus heavily, for example, and its the default audio codec for webm video files. It's also very popular for real time audio like in video conferencing.
This needs to be more widely shouted, Opus derives from CELT which was primarily focused on low latency audio encoding (which mp3 really sucks at) and it's the defacto standard for VoIP. Although for professional applications like wireless companies will use their own proprietary codecs.
https://podcast-standard.org/audio/
"Spotify for Podcasters" is the biggest hosting service pushing AAC usage, with ~30% of their inventory being AAC. https://podcast-standard.org/hosting_systems/spotify/